Aim: To ascertain the prevalence of calcium pyrophosphate arthritis (CPPA) at diagnosis and during follow-up of patients with gout. Methods: Inception cohort of patients with gout prospectively recruited and followed-up from 1994–2023. Gout-case was defined as crystal-proved tophus or arthritis, or the presence of tophus plus double contour with ultrasonography. CPPA was defined as the presence of intra-leukocyte calcium pyrophosphate (CPP) crystals in synovial fluid (SF) and neat chondrocalcinosis in plain radiographs. Age, gender, time from onset of symptoms, number of flares, joint distribution, previous and prescribed treatments, colchicine prophylaxis, comorbidities, alcohol intake, use of diuretics, renal function, and previous vascular disease were available for analysis. Results: A total of 1,544 patients with gout, with an average of 4-year follow-up, were available for analysis. CPPA was observed in 127/1,544 cases (8.2%). In 37/1,544 patients (2.4%) CPP and monosodium urate (MSU) crystals were observed in the same SF sample at gout diagnosis, and 90/1,544 (5.8%) showed CPP crystals apart from the diagnosis of gout. CPPA-gout cases had more flares per year, but no more frequent polyarticular distribution at baseline compared to non-CPPA-gout. CPPA-gout cases were older at baseline and showed lower renal function. Women, patients using diuretics, patients with hypertension, and those with previous vascular events showed CPPA more frequently. Multivariate analysis showed that only age and use of diuretics were independently associated with CPPA, as other variables apparently associated were dependent on aging. Interestingly, an analysis of the prevalence in the three decades available showed an increased CPPA diagnosis through time, probably associated with increased awareness of the association. Conclusions: (1) CPPA is not infrequent in patients with gout; (2) it is associated with aging and diuretic use; (3) awareness of this association may increase the rate of diagnosis.
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